Cerebrospinal fluid (CSF) is a clear, colorless fluid that is primarily produced by the choroid plexus and surrounds the brain and spinal cord. CSF constantly circulates through the ventricular system of the brain and is ultimately absorbed into the bloodstream. CSF has three important functions. First, because CSF keeps the brain and spinal cord buoyant, it acts as a protective cushion or “shock absorber” to prevent injuries to the central nervous system. Second, CSF acts as the vehicle through which nutrients are delivered to the brain, and conversely, as the vehicle through which waste products are carried away from the brain tissue. Finally, by flowing between the cranium and the spine, CSF can compensate for changes in the amount of blood found in the brain.
Hydrocephalus is a neurological condition that is caused by the abnormal accumulation of CSF within the ventricles, or cavities, of the brain. Hydrocephalus, which affects mostly infants and young children, arises when the production of CSF exceeds the absorption of CSF into the bloodstream. This is usually the result of some type of blockage in the brain that prevents the normal flow of fluid. Such blockage can be caused by a number of factors, including, for example, genetic predisposition, intraventricular or intracranial hemorrhage, infections such as meningitis, head trauma, or the like. Blockage of the flow of CSF consequently creates an imbalance between the amount of CSF produced by the choroid plexus and the rate at which CSF is absorbed into the bloodstream, thereby increasing pressure within the ventricles in the brain, which causes the ventricles to enlarge.
Hydrocephalus is often treated by draining cerebrospinal fluid accumulated in the ventricles from the brain using a hydrocephalus shunt catheter inserted through the skull and into the ventricles. The catheter drains the fluid away from the brain and delivers it to another part of the body, such as the peritoneum or the superior vena cava. The catheter may employ a flow-limiting device such as a differential pressure valve, referred to as a shunt valve, to maintain a physiological pressure within the ventricles.
Prior to implantation of a hydrocephalus shunt, an external drainage system is used to control pressure within the ventricles. External drainage systems are also used to assess patient response to CSF drainage, to evaluate the brain compliance to determine the appropriate shunt pressure setting, to treat infection, to drain blood laden CSF, to monitor intracranial pressure (ICP), and while awaiting patient stabilization. External drainage systems typically include a support member, e.g., an IV pole, having a moveable drip assembly with a disposable bag adjustably fastened to the support. The flow of cerebrospinal fluid from the patient's brain can be controlled by elevating or lowering the drip assembly to alter the resistance of the fluid pathway from the brain ventricles into the drip assembly. This provides a means of controlling the pressure within the ventricles.
External drainage systems are often provided with a scale movably mated to the support member for determining and controlling the ICP of the fluid in the patient's ventricles. In order for the scale to accurately reflect the true ICP of the patient, a zero pressure point on the scale must be aligned at the same height as a zero reference point on the patient, such as a point corresponding to the position of the patient's Foramen of Monro. Because this is not a visible point, the external auditory canal is often used as a convenient external landmark. Once the zero pressure point on the scale is determined by aligning the zero pressure point on the scale with this landmark, the drip assembly can be adjusted with respect to the zero pressure point in order to control the flow of fluid from the patient's ventricular system into the drip assembly, and thereby control ICP.
A variety of techniques for measuring and aligning the zero reference point on the patient with the zero pressure point on the scale are known. Laser pointers, for example, are used by attaching the laser pointer to the scale on the EDS, or positioning it adjacent the scale. The laser is then activated, and the height of the laser is adjusted until the laser light aligns with a zero reference point on the patient, such as a position corresponding to the auditory canal. The zero pressure point on the scale is then marked, or alternatively the scale is positioned to align the zero pressure point marked on the scale with the zero reference point on the patient, for the duration of use of the external drainage system. The drip assembly can then be adjusted with respect to that reference pressure point in order to increase or decrease the ICP, and thereby increase or decrease the flow of fluid from the patient's brain. While such laser devices have proven effective, it can be difficult to ensure that the laser beam is horizontally level. Additional drawbacks of laser devices include the costs and need to power such devices, as well as any potential risks that may result from shining a laser beam directly at a patient.
Another prior art device that is used for determining the zero pressure point is a telescoping antenna with a leveling bubble. The antenna is extended from the support member to the zero reference point on the patient, and the leveling bubble is used to horizontally position the antenna. Another similar prior art device is a large L- or T-square which is held perpendicular with respect to the vertical support member, and horizontal with respect to the patient. Drawbacks of these devices include the need for the patient to be relatively close to the support member, as well as the possible risk of injuring a patient with the device while positioning the device adjacent the patient's zero reference point. Such devices can also be awkward to handle, as they often require one person to hold the T- or L-square, while another person adjusts the height of the drainage system. Moreover, T- and L-square devices are often very large, and require sizable storage spaces.
Accordingly, there exists a need for a safe, accurate, and easy to use leveling device for determining the zero pressure point of an external draining system with respect to a patient.